1. Field of the Invention
This invention relates to a projection-type display system, and particularly to a field sequential color projection display system.
2. Description of Prior Art
LCD projection systems demand high brightness, high accuracy, excellent image quality and low cost, as well as compact size.
In an LCD projection system, the light source has to be effectively used in order to provide high brightness, thus requiring the use of a P/S converter and micro-lens and so on. A reflective-type LCLV (liquid crystal light valve) can further improve the image brightness and accuracy. Smaller LCD panels facilitate reducing the volume of the optical engine. However, the optical design and the cost of the system tend to trade-off with quality. It is difficult to provide a good quality LCD projection system at a low cost.
The prior arts, such as the three-panel LCD system disclosed in U.S. Pat. No. 4,904,061 by Aruga and the three-panel projection data monitor disclosed in IBM J. Res. Develop. Vol. 42, No. 3/4, 1998, by R. L. Melcher et al., can provide high light efficiency and high accuracy. However, in order to reduce the volume of the optical engine of an LCD system and simplify the optical design, two-panel or one panel LCD systems have been used to replace three-panel system without degrading the image quality. For example, referring to FIG. 1, U.S. Pat. No. 5,517,340 of Doang et al. passes the light emitted from the light source 13 through the polarizing color filter 16 and the broadband polarizing beam-splitting prism 12 so that s-polarized and p-polarized R, G, B light beams are sequentially incident to two reflective-type LCLVs 10 through two neighboring surfaces of the prism. The light beams reflected by the LCLVs 10 are combined by the prism 12 to form a single light beam, which passes through the projection lenses 14 to present a full-color image.
The applicant has disclosed a two-panel reflective-type ferro-electric LCLV system in Taiwanese Patent Application entitled xe2x80x9cField Sequential Dichroic Light Valvexe2x80x9d. Referring to FIG. 2, the system comprises: a first right-angle prism 20 for guiding the incident light beam; a second right-angle prism 24 for reflecting the light beam to the polarizing beam-splitting prism; a rotary disk 22 for disposing R, G, B color filters to respectively pass only R, G. B light beams; a spindle motor 23 for driving the rotation of the rotary disk 22; a broadband polarizing beam-splitting device 26 for respectively transmitting and reflecting the p-polarized light and the s-polarized light of sequentially produced R, G, B light beams; two fast time response LCLVs 28, 29 for receiving and reflecting the p-polarized light and the s-polarized light of the R, G, B light beams, respectively, so that the p-polarized light is converted to s-polarized light and the s-polarized light is converted to p-polarized light; and projection lenses 30 for projecting the light beam to a screen after the s-polarized light and the p-polarized light respectively reflected by the LCLV 28 and 29 are reflected and transmitted by polarizing beam-splitting device 26. This system is characterized in that the color filters are disposed on the disk. Since the response time of the ferroelectric liquid crystal panel is one thousand times faster than that of a TN (twisted neumatic) type LCLV, the images of s-polarized light and p-polarized light can be simultaneously displayed on the screen. The energy of the light source is therefore effectively used.
Another two-panel system disclosed by ITRI uses a beam splitting device including a color wheel and dichroic mirrors to simplify the optical engine.
Since the response time of ferroelectric LCLV is very fast, using a single panel incorporating the use of a fast field sequential beam splitting/combining component can obtain full-color projection display. For the prior arts shown in FIG. 1 and FIG. 2, using a light source having a linear polarization can easily simplify the two-panel system to a single-panel projection display system. However, the mechanical behavior of the color disk deteriorates the stability of optical engine.
In U.S. Pat. No. 5,347,378, M. A. Handschy et al. disclose a display device as shown in FIG. 3, in which a structure having serially arranged color selective ferroelectric liquid crystal components 40 performs fast time sequential switching, incorporating the use of a monochromatic display panel 32 to form a full-color display system. However, this device uses many polarizers 34, 36, 38 and 42, which absorb a significant part of the light energy.
It is noted from the above description of the prior arts that it is desirable to combine a fast field sequential beam splitting/combining device, optical design with improved light efficiency, and a single panel fast response LCLV.
Accordingly, the object of this invention is to provide a field sequential color projection display system, which has high brightness, high accuracy and compact size, and is light and energy-saving.
To achieve the above object, this invention uses a fast response light valve, incorporating the beam splitting/combining theory of optical thin film to design a field sequential color projection display system including a single panel LCLV.
Compared with the conventional one-panel LCLV display system or the ferroelectric LCLV display system incorporating a color disk, the field sequential color projection display system of this invention can use the light energy more efficiently and has no drawback due to the mechanical behavior of the color disk.
Moreover, since the ferroelectric LCLV used in this invention has a diagonal dimension shorter than 1 inch and the prism module is compact, the volume of the optical engine is reduced relative to the prior art.
In the field sequential color projection display system of this invention, since the multi-layer thin film of the beam splitting/combining module is a polarizing mechanism, the system does not need to use a front polarizing device for the incident light beam. Thus, the optical engine is simplified and the volume of the system is reduced. Furthermore, the field sequential color projection display system of this invention has a structure good for mass production, providing a high utility for the relevant industry.